(a) Field of the Invention
The present invention relates to a liquid crystal display having a wide viewing angle.
(b) Description of the Related Art
A liquid crystal display (LCD) includes two substrates and a liquid crystal layer interposed therebetween. The transmittance of the incident light is controlled by the strength of the electric field applied to the liquid crystal layer.
A vertically aligned twisted nematic (VATN) liquid crystal display has a couple of transparent substrates which have transparent electrodes respectively on their inner surfaces, a liquid crystal layer between two substrates and a couple of polarizers which are attached to the outer surfaces of the substrates respectively. In off state of the LCD, i.e., in the state that the electric field is not applied to the electrodes, the long axes of the liquid crystal molecules are perpendicular to the substrates. On the other hand, in on state of the LCD, i.e., in the state that the sufficient electric field is applied to the electrodes, the long axes of the liquid crystal molecules are parallel to the substrates and twisted spirally with a constant pitch from the inner surface of one substrate to that of the other substrate, and thus the orientation of the long axes of the liquid crystal molecules vary continuously.
The VATN LCD operating in normally black mode may have an off state which is sufficiently dark because the liquid crystal molecules are aligned perpendicular to the substrates in the off state. Therefore, the contrast ratio is relatively high compared with the conventional TN LCD. However, the viewing angle of the VATN LCD may not be so wide due to the difference among retardation values in various viewing directions.
It is therefore an object of the present invention to widen the viewing angle of an LCD.
These and other objects, features and advantages are provided, according to the present invention, by a liquid crystal display having protrusion patterns on transparent electrodes for forming multi-domains in plane view.
A liquid crystal display, according to one of embodiments of the present invention, comprises a first substrate including a common electrode and a first protrusions formed on the common electrode and a second substrate opposite the first substrate, the second substrate including a pixel electrode located at a position corresponding to the common electrode and a second protrusion formed on the pixel electrode, wherein the first and the second protrusions are arranged alternately and a distance between end portions of the first and the second protrusions is less than a distance between remaining portions of the first and the second protrusions. The width of the first and the second protrusions may be in the range of 3-20 xcexcm, and the height of the first and the second protrusions may be in the range of 0.3-3.0 xcexcm.
A liquid crystal layer having negative dielectric anisotropy may be interposed between the substrates, and alignment layers may be formed on inner surfaces of the substrates respectively.
A pair of polarizers may be attached to outer surfaces of the substrates, and the polarizing directions of the polarizers are preferably perpendicular to each other.
Compensation films may be attached between one of the substrates and one of the polarizers attached thereto, and a biaxial or a combination of an a-plate and a c-plate compensation films may be used. The slow axis of the biaxial or the a-plate compensation film is preferably parallel or perpendicular to the polarizing directions of the polarizers.
The second protrusion may have a saw shape in plane view and the first protrusion may include a first portion having a saw shape parallel to the second protrusion and a second portion formed at a position corresponding to the boundary of the pixel electrode where an angle between the second protrusion and the boundary of the pixel electrode is an acute angle. A third protrusion extending from the convex point of the first saw shape portion to the second protrusion may be formed on the common electrode, and a fourth protrusion extending from the convex point of the second saw shape protrusion to the first protrusion may be formed on the pixel electrode. The first portion of the first protrusion and the second protrusion may be bent once in a unit pixel region.
The first protrusion may form a substantially tetragonal ring in plane view, and the second protrusion may be formed at a position corresponding to the center of the tetragonal ring. The first protrusion preferably forms a substantially regular tetragonal ring, and the first protrusion may be broken at midpoint of each side of the tetragon. The second protrusion may have a cross shape in plane view. The number of the first and the second protrusions may be equal to or more than one. The polarizing-directions of the first and the second polarizers are parallel to transverse and longitudinal directions of the first protrusion respectively.
Protrusion ratio and luminance increases if a portion of the first protrusion is formed outside of a portion corresponding to the pixel electrode in plane view.
When the first and the second substrates are viewed from the top, a region defined by the first and the second protrusions forms a substantially closed polygon, and angle made by the protrusion on one substrate is an obtuse angle. In addition, a long diagonal in a region defined by the first and the second protrusions is a diagonal substantially perpendicular to the liquid crystal director in the regions while a voltage is applied to the pixel electrode and the common electrode and when the first and the second substrates are viewed from the top.
A saw shape protrusion may be formed on a pixel electrode and a gate wiring in the thin film transistor (TFT) substrate may overlap the protrusion in plane view. In the color filter substrate, a saw shape protrusion formed on the common electrode and a black matrix overlapping the protrusion may be formed.
The black matrix may include a portion put across the bent points of the first and the second saw shape protrusion and a triangular portion covering a portion that the first and the second protrusions meet a boundary of the pixel electrode in plane view.
The black matrix may include another portion overlapping the first protrusion instead that the gate wiring overlaps the first protrusion in plane view.
On the other hand, a first and a second saw shape protrusions parallel and alternate to each other are formed on the common electrode and the pixel electrode respectively, and the pixel electrode may have a saw shape which is convex between points where the first and the second protrusions meet the pixel electrode. The angle between the first protrusion and a boundary of the pixel electrode near the saw shape convex portion is preferably equal to or more than 90xc2x0.
The pixel electrode may have a saw shape surrounding the first and the second protrusions in plane view.
By forming protrusions on the transparent electrodes in above-described way, a liquid, crystal layer between two electrodes are divided to four regions that the directors of the liquid crystal layer have different angles when a voltage is applied to the electrodes, thereby viewing angle is widened and disclination is removed.